Study On The New Process And Mechanism Of Preparing Adipic Acid From Benzene

Adipic acid (AA) is one of the important basic organic chemical materials, which is mainly used in the production of nylon-66fibers, engineering plastics and polyurethanes, etc. With the extensive application of nylon in automobile industry, demand of AA has been growing significantly in recent years and is expected to grow in the next years. At present, the main starting material for synthesis of AA is benzene, from which two routes have been developed. The first is the cyclohaxane route and the second is the cyclohexene route.In this paper, studies have been carried out concerning the catalytic reactions of partial hydrogenation of benzene, hydration of cyclohexene and nitric acid oxidation of cyclohexene to AA, which are involved in the production of AA from benzene, the research results are summarized as followings:1. Partial hydrogenation of benzene to cyclohexenePartial hydrogenation of benzene to cyclohexene is thermodynamically unfavorable. In order to obtain high selectivity of cyclohexene, a specific catalytic system has been employed, i.e., in the presence of water, using Ru as the main catalyst and refinery metal oxides (such as ZrO2) as dispersant and transition metal salts (such as ZnSO4) as additive. The reaction is generally carried out at pressure of5MPa and at temperature of150℃.Though the transition metal salts play an important role for the enhancement of the cyclohexene selectivity, there are still many aspects unclear concerning the mechanism. In this paper, the Ru catalyst is synthesized by classical precipitation method; the influence of some transition metal ions (Zn2+, Fe2+, Ni2+, Cr3+, Mn2+and Cd2+) on the performance of Ru is investigated in a stainless steel and a titanium autoclave respectively. The catalysts were characterized using XRD, BET surface area measurement and XPS. The structure configurations and formation enthalpies of the hydrated metal ions, the complexes of the metal ions with benzene and cyclohexene as well as the complexes of hydrated metal ions with benzene and cyclohexene were optimized and evaluated using quantum chemical calculation methods. Based on the obtained results, the mechanism of the influence of the transition metal ions on the performance of the Ru catalyst was suggested.2. Hydration of cyclohexene to cyclohexanolThe hydration of cyclohexene to cyclohexanol is catalyzed by ZSM-5zeolite. A suitable ZSM-5zeolite has to be synthesized for this reaction in order to obtain satisfactory performance. In this paper, pre-crystallization method is used for synthesis of ZSM-5zeolite and its catalytic performance in the hydration of cyclohexene to cyclohexanol is investigated in a500ml stainless steel autoclave. Optimal ZSM-5zeolite synthesis conditions and reaction conditions have been obtained. The conversion of cyclohexene and the selectivity of cyclohexanol amounted to12.65%、99.54%respectively. Also the catalyst was characterized in terms of SEM, XRD, BET specific surface area measurement and chemical adsorption of NH3. Based on the above results, studies concerning the amplified production of the zeolite in100L autoclave, recovery of the mother liquio produced fron the synthesis of zeolite process and resuse of the zeolite in the reaction process were also carried out.3. The nitric acid oxidation of the cyclohexanolThe nitric acid oxidation of the cyclohexanol is a complicated process involving many reaction intermediates. This reaction is generally conducted at60-80℃with50-60%nitric acid. To improve the selectivity of AA, Cu2+and V5+are employed as catalysts. Though this process has been industrialized for many years, the influence of the catalysts on the product selectivity has not been systematically investigated; also the reaction kinetics at conditions close to industrial operation has not been obtained. In this paper, the reaction kinetics of oxidation reaction of cyclohexanol to AA by nitric acid is studied in a CSTR reactor with and without using Cu2+and V5+as catalysts at conditions close to the industrial operation. According to the characteristics of the reaction, rate equations of power law type and lumping of the reaction intermediates are used for the regression of experimental data; and the values of the parameters in the rate equations have been obtained. Based on the experimental results and the analysis of the reference papers, the way for the catalysts to influence the reaction mechanism was proposed.